The invention includes embodiments that relate to a device. More particularly the invention includes embodiments that relate to a light-emitting device and a method of making the device.
An organic light-emitting device (OLED) may be used for flat panel backlight applications or for general illumination. OLED generates light through radiative recombination of excitons on electrically excited organic molecules. OLEDs can be used for both display and lighting application. Typically, one of the electrodes in an OLED may have the property of being both transparent and conductive. A commonly used material for such transparent electrode is a transparent conducting oxide (TCO), for example, indium tin oxide (ITO) or aluminum-doped zinc oxide (AZO). When compared with metals, TCOs have much higher electric resistivity. Combined with the fact that OLEDs are current driven, the higher electric resistivity of TCO transparent electrode may cause a significant voltage change over large OLED pixels. When the TCO electrode is large in size for example, having a length of about 10 centimeters and a breadth of about 10 centimeters, the voltage change may be significant and may cause significant change of light intensity over the device. To overcome the high resistivity of TCO transparent electrode and still be able to make large OLED pixels, one approach is to divide the desired large area OLED device into separate smaller emitting pixels connected monolithically in series. The TCO electrode may be pixelized to small size (for example, 1 centimeter in current flow direction) so that the voltage change and hence the light intensity change over each pixel is not significant to a viewer. Due to the series electrical connection nature, the areas between the pixels where the monolithic series connections are located may not emit light. These areas can form the dark areas on the OLED surface thus forming a contrast between the area where light is emitted (an emissive area) and the dark areas (non-emissive areas). Many display and lighting applications may require that no dark area be seen when the OLEDs are powered.
For interior/exterior decorations and signage, it may be desirable to obtain a desired color output. It may be desirable to have a device which can provide efficient light output over the entire OLED and reduce the contrast between emissive area and non-emissive area to provide a uniformly lit OLED device.